After 50 years, the Saigon execution remains one of the defining images of the war. Time magazine has declared it one of history’s 100 most influential photos.

“It still represents a lot of what photojournalists do, that idea of bearing witness to an important event,” said Keith Greenwood, a University of Missouri photojournalism-history professor. “There are ugly things that happen that need to be recorded and shared.”

It was the second day of the Tet Offensive. North Vietnamese forces and Vietcong guerillas had attacked South Vietnamese towns and cities, including the capital Saigon, during a holiday ceasefire.

Adams, a former Marine Corps Korean War photographer who joined the AP in 1962, and NBC cameraman Vo Suu had been checking out fighting in a Saigon neighbourhood when they saw South Vietnamese soldiers pulling a prisoner out of a building, towards the newsmen.

Public support for the war started to wane after the Tet Offensive. Picture: AP Photo/Nick UtSource:AP

Instead, Loan fired, and Adams’ photo froze the moment in time when prisoner Bay Lop faced death. Suu’s footage also captured the moment, in motion.

Loan told the two, “They killed many of my men and many of your people,” and walked away, Adams recalled in a 1998 interview for an AP oral history project.

At the AP’s New York headquarters, photography director Hal Buell saw the image emerging from the radio-based system used to transmit photos at the time. After some deliberation, he and other editors decided to distribute it worldwide.

“I knew when it went out that you were going to get two reactions. The doves were going to say, ‘See the kind of people we’re dealing with here (in South Vietnam)?’ And the hawks said, ‘It shouldn’t have been used — you guys gotta get on the team,”’ said Buell, now retired.

But, he said: “The image had an impact and its impact was felt by those people who were on the fences.”

The photo appeared on front pages, TV screens and protest placards. The Tet Offensive proved a military failure for the Communists, but it fuelled the American public’s pessimism and weariness about the war. It ended when the North prevailed in 1975.

Adams, meanwhile, felt Loan was unfairly vilified by a public that didn’t see something outside the frame — the killings of Loan’s aide and the aide’s family just hours earlier by the Vietcong.

“I don’t say what he did was right, but he was fighting a war, and he was up against some pretty bad people,” Adams said.

Adams also captured other historic moments — such as this scene where Apollo 11 astronauts were welcomed in New York. Picture: AP Photo/Eddie Adams, fileSource:Supplied

He rued that “two people’s lives were destroyed that day” — Lop’s and Loan’s — “and I don’t want to destroy anybody’s life. That’s not my job”.

Loan died in 1998 in Virginia, where he ran a restaurant. Lop’s widow told the AP in 2000 that she felt the picture helped turn Americans against the war.

Adams, who died in 2004, was more proud of his 1977 photos of people fleeing post-war Vietnam.

Those images helped persuade the US government to admit over 200,000 of the refugees (one of the pictures also is on the Time list). His legacy includes the annual Eddie Adams Workshop for emerging photojournalists, which has been running for 30 years. Work and fundraising are underway to expand a 2012 short documentary about the famous photograph, Saigon ’68, into a full-length film.

Director Douglas Sloan says it will encourage people to understand the context of what they see in powerful images.